%I
%S 1,2,9,30,90,248,650,1560,3560,7680,15786,31076,58905,107768,191180,
%T 329664,554038,909558,1461655,2302950,3563482,5422392,8124040,
%U 11997648,17482295,25156872
%N Number of multigraphs on 4 unlabeled nodes with n edges where the edges can be of two colors.
%t Needs["Combinatorica`"];n = 4; nn = 25; CoefficientList[Series[PairGroupIndex[SymmetricGroup[n], s] /.Table[s[i] > 1/(1  x^i)^2, {i, 1, Binomial[n, 2]}], {x, 0, nn}], x]
%Y Cf. A050531.
%K nonn
%O 0,2
%A _Geoffrey Critzer_, Aug 10 2015
